Jamestown Canyon virus, a California serogroup bunyavirus, has very recently been implicated as a cause of encephalitis in humans. Virus isolations from arthropods and serologic surveys indicate this virus has a nation-wide distribution. The Principal Investigator has shown that current diagnostic procedures are inadequate to detect Jamestown Canyon virus infections in humans. Thus, the true epidemiological impact of this agent on human health remains to be ascertained. Preliminary studies have established a base for the proposed study in northern Indiana and southwestern Michigan. Jamestown Canyon virus utilizes white-tailed deer, Odocoileus virginianus, as its primary vertebrate host. However, virtually nothing else is known of the natural cycle. The primary arthropod vector has not been incriminated. The specific aim of this proposal is to describe the basic natural cycle of Jamestown Canyon virus. Five specific objectives in this proposal focus on (1) the seasonal succession of hematophagous arthropods in enzootic foci, (2) virus isolations and infectivity rates from arthropods, (3) host associations between deer and potential vectors, (4) the determination of mode of transmission of Jamestown Canyon virus by vectors to vertebrate hosts, and, (5) serologic surveys of deer and humans to identify additional enzootic foci, the periodicity of virus circulation, and identification of the specific human disease syndrome. Long-term objectives include 1) a description of the complete natural cycle of Jamestown Canyon virus, 2) the ecology and vector competence of principal arthropod vectors to deer and humans, and, 3) expanded epidemiological investigations of the Midwestern human population to map Jamestown Canyon virus foci of infection.